Cross Determination of Exciton Coherence Length in J-Aggregates.

The coherence length of the Frenkel excitons ( N coh ) is one of the most critical parameters governing many key features of supramolecular J-aggregates. Determining experimentally the value of N coh is a nontrivial task since it is sensitive to the technique/method applied, causing discrepancies in the literature data even for the same chemical compound and aggregation conditions. By using a combination of different experimental techniques including UV-vis-NIR, fluorescence emission, time-resolved photoluminescence, and transient absorption spectroscopies, we determined N coh values for J-aggregates of a cyanine dye. We found that the absorption spectroscopy alone - a widely used technique- fails in determining right value for N coh . The correct approach is based on the modification of photoluminescence lifetime and nonlinear response upon aggregation and careful analysis of the Stokes shift and electron-phonon coupling strength. This approach revealed that N coh of JC-1 J-aggregates ranges from 3 to 6.